Ethanol nowadays is an important product for its high demand in the fuel market. Its market grew from less than a billion liters in 1975 to more than 39 billion liters in 2006 and is expected to reach 100 billion liters in 2015 (Licht 2006). Global ethanol production is more than doubled between 2000 and 2005, while production of biodiesel, starting from a much smaller base, expanded nearly fourfold. By contrast, world's oil production is increased by only 7 percent during the same period. Less than 4% of ethanol is produced synthetically from petroleum, while the rest is produced by fermentation from bioresources. Ethanol is now produced from two major groups of bioresources: sugar substances and starchy materials. There is a competition between these two feedstock for fuel ethanol production. Sugar substances were the feedstock for more than 60% of fuel ethanol production at the beginning of the 2000s, its share decreased to 47% by 2006, when grains accounted for 53% of the production (Licht 2006, “World ethanol markets: The outlook to 2015,” Tunbridge Wells, Agra Europe special report, UK).
The production and use of biofuels have entered a new era of global growth. The two primary biofuels in use today are ethanol and biodiesel. Ethanol is readily blended with gasoline, and biodiesel is blended with petroleum-based diesel for use in conventional diesel-fueled engines. Ethanol currently accounts for more than 90 percent of total biofuels production, with biodiesel making up the rest. Ethanol has a potential market as big as the oil market. It can potentially replace the entire fuel market for gasoline. Methanol or ethanol is also used for manufacture of biodiesel, during the process of transesterification.
Nearly, all fuel ethanol is produced by fermentation of corn sugar and sugarcane wastes. The amounts of sugar substances and grains are limited in the world and they are relatively expensive feedstocks for ethanol production. Bioethanol production using these substances results in competition with human food which may lead to increase in the price of grains and sugar to higher levels in the future. Ethanol-based biofuels are generally derived from fermenting the carbohydrates present in corn and soy, which are cheap to produce. However, cultivating these crops, require huge area of land that can displace acreage required for food.
Due to limited availability of agricultural land, it is essential that we do not ignore the potential of the marine environment as a source of biomass for ethanol production. It is known that macroalgae may be cultivated easily, grow prolifically and sequester carbon. In addition, the aquaculture of seaweeds reduces contribution to eutrophication of the seas and therefore may be used to mitigate the effects of sewage effluent and industrial sources of nitrogenous waste such as those originating from fish aquaculture, contributing to the maintenance or improvement of biodiversity.
Macro algae, more commonly known as “seaweeds”, are diverse group of fast growing marine plants and occur as attached forms to rocks in both intertidal as well as shallow subtidal waters. These plants being autotrophic, use energy from the sun to combine water with carbon dioxide (CO2) to produce carbohydrates and ultimately biomass. This biomass is harvested throughout the world as a food source as well as export materials for the production of phycocolloids. Seaweeds are cultivated commercially in several Asian countries such as China, Japan, Philippines and Korea since the demand for seaweeds and seaweed based products outstripped the supply from wild stocks. Further, the increase in demand started to spur research and development of culture methods as well as extraction processes for sustainable production and utilization of seaweed resources. These seaweeds can be grown on commercial scale in the sea where area is unlimited and huge biomass can be generated without precise agricultural practices.
These seaweeds can be used for biofuel production, specifically for bioethanol production as they are more appropriate for bioethanol production as compared to biodiesel production for following reasons.                1. Carbohydrate content of some of the seaweeds is very high.        2. The lipid (oil) content in seaweeds is less as compared to carbohydrate content which makes them less suitable for biodiesel production.        3: For ethanol production, dry/semidry or fresh seaweeds can be used. They do not require any pretreatment like drying.        4. Extraction of oil is required for biodiesel production, for which the material needs to be dried which is energy incentive.        5. CO2 generated through ethanol fermentation can be used as algae feedstock.        
Red algae are globally important seaweeds having high growth rate. They are representatives of diverse origin; more complex thalli are built up of filaments. The red algae Kappaphycus and Betaphycus are now the most important sources of carrageenan used in food industry. Gracilaria, Gelidium, Pterocladia and other red algae are used in the manufacture of agar, widely used as a gelling agent in growth medium for microorganisms and for biotechnological applications. These algal cell walls are made up of long chain polysaccharides like cellulose and agars/carrageenans having widespread commercial use.
Carrageenan is a family of linear sulphated polysaccharides extracted from red seaweeds of Kappaphycus and Betaphycus. Carrageenan is made up of sodium, potassium, magnesium and calcium sulfate esters of galactose and 3,6-anhydrogalactose units. Three basic types of carrageenan are available, which differ in the numbers and location of sulfated ester. These polysaccharides are large, highly flexible molecules, which curl around each other forming double helical structures in the presence of monovalent and divalent cations. This gives them the ability to form a variety of thermo-reversible gels at room temperature. Carrageenan content varies from 25-35% on dry weight basis in different carrageenophytes. Carrageenan is widely used in the food and pharmaceutical industries as thickening, stabilizing and gelling agents.
Until recently, the seaweed industry in India had relied exclusively on harvesting of the natural stock. Primarily, this had focused on Sargassum (for alginates and liquid seaweed fertilizer), Gracilaria edulis (for low grade agar) and Gelidiella acerosa (for moderately superior grade agar). All this has undergone a dramatic change over the last five years. On the one hand, Kappaphycus alvarezii was adapted in Indian waters and its cultivation is demonstrated to be viable as a result of a decade long research (U.S. Pat. No. 6,858,430 dated Feb. 22, 2005). The technology was subsequently licensed by CSMCRI which, in turn, has spurred the cultivation activity in Tamil Nadu by self help groups and NGOs with buy back guarantee from the end user. Over the past twenty years, large-scale cultivation of carrageenophytes is successfully carried out all over the world including India and hence there is no shortage of carrageenan yielding seaweed. Given the fact that seaweeds contain water more than 90% on fresh weight basis, CSMCRI invented a unique process (U.S. Pat. No. 6,893,479) of liquefying the fresh seaweed without adding any water. Through this simple process, two products could be recovered in an integrated manner, one being a concentrated residue rich in •-carrageenan and the other being the plant sap (liquid seaweed fertilizer-LSF) rich in major and minor plant nutrients. To fulfill the demand of agriculture, massive biomass of Kappaphycus alvarezii is required which can be achieved through on shore and off-shore cultivation. After recovery of sap, large amount of residual biomass rich in carrageenan will be generated. Once raw material requirement for k-carrageenan is satisfied, the residual biomass can be used for bioethanol production. Thus, recovery of multiple products from seaweed would make cultivation economically more viable. Good cultivation practices may prove Kappaphycus, a cheaper raw material, for ethanol production. These developments are of vital importance from the perspective of massive expansion of the seaweed based industries while at the same time focusing on sustainability.
A major criticism often faced against large-scale fuel production using food crop's, is that it could divert agricultural production away from food crops, especially in developing countries. The fact is that energy-crop programmes compete with food crops with respect to use of agricultural land, water, fertilizers, skilled labour etc. which leads to increase in food price. Also, cultivation of crops for biofuel production will have impacts on biological diversity. Hence there is an urgent need to identify an alternative source for bioethanol production which overcomes all the limitations. Marine algae/seaweeds is the ideal option as they grow in the sea, where vast area for cultivation is available and due to high growth rate, generates huge biomass without special agricultural practices, thus, reducing the pressure on agricultural land. Apart from these, they are rich in carbohydrates and hence ideal source for bioethanol production.